It has been shown that in equine abortion virus (EAV) infection an unusual relationchip between cellular and viral DNA synthesis exists such that viral DNA synthesis apparently is initiated only in cells which have reached S-phase of the cell cycle. Major areas of investigation in this study are 1) Is the relationship between EAV DNA synthesis and S phase of the cell cycle associated with periodic activity of cellular enzymes associated with DNA synthesis? 2) What is the pattern of synthesis of proteins binding to DNA in synchronized KB cultures and what alterations in the synthesis of these proteins takes place during EAV infection? 3) In cultures infected at different phases of the mitotic cycle what patterns of transcription of viral m- RNA occur? 4) Is the initiation of EAV DNA synthesis related to the events which occur during the transition from G1 to a cell "activated" for DNA synthesis?